1. Field of the Invention
The present invention relates to a structure for connecting an ignition coil and a spark plug for use in an internal combustion engine.
2. Description of the Background Art
Referring to FIGS. 6 and 7, a spark plug 51 mounted in the bottom of a plug hole H formed in a cylinder head C and an ignition coil 52 fixed on the cylinder head C are electrically connected in a manner to be described below.
A connecting terminal 53 projecting downwardly from the underside of the ignition coil 52 is electrically connected to a terminal 54 of the spark plug 51 which projects upwardly in the cylinder head C through a conductive member 55 such as a single spring, a metal round bar, and a metal cylinder. An insulating member 56 covers an outer periphery of the conductive member 55 to extend from the connecting terminal 53 to the terminal 54.
There are two types of insulating members 56. One type is an insulating member comprised of three members: a cap for covering the range from the connecting terminal 53 to the conductive member 55, a bushing for covering the range from the terminal 54 to the conductive member 55, and a sleeve for covering the conductive member 55 to extend from the cap to the bushing. The other type is an insulating member comprised of the cap, bushing and sleeve which are formed integrally. In either case, the cap or a portion corresponding to the cap is fitted in an upper portion of the plug hole C in such a manner that an upper surface thereof is in intimate contact with the underside of the ignition coil 52 and an outer periphery thereof is in intimate contact with an inner peripheral surface of the plug hole H.
A first air vent hole 57 is formed in the contact portion between the upper surface of the cap or the portion corresponding to the cap and the bottom surface of the ignition coil 52 and extends from the outer edge of the contact portion. A second air vent hole 58 for communication between the first air vent hole 57 and the interior of the plug hole H is formed in the cap or the portion corresponding to the cap.
When the air in the plug hole H is heated to expand, the expanded amount of air may be escaped through the first and second air vent holes 57 and 58, preventing changes in pressure in the plug hole H.
The above stated connecting structure presents no significant problem when the cylinder head C is exposed to a small amount of water. However, when the cylinder head C is subjected to high-pressure water, for example, during car washing, water might enter the plug hole H through the first and second air vent holes 57 and 58.